1. Field of the Invention
The present invention relates generally to manually operated air pumps, such as bicycle pumps, and more particularly to manually operated pumps having a low pressure mode and a high pressure mode.
2. Description of the Prior Art
The operator of a manual air pump, such as a bicycle tire pump, generally encounters two difficulties in pumping a pneumatic article as a tire to a high pressure, such as more than 100 psi. Firstly, when commencing the pumping process, the article has a low (ambient) pressure and it is desirable to pump as large a volume of air into the article with each pumping stroke. The operator's difficulty at this stage is that many pumping strokes are required unless the volume of air per stroke is large. Secondly, when the article approaches a relatively high pressure, perhaps in excess of 80 psi, the operator generally encounters difficulty in pumping further air into the article due to the force required. In this stage of the pumping operation, it is desirable for the pump to have a relatively narrow bore, such that the force required of the operator to operate the pump is manageable. Therefore, dual mode manual pumps have been developed which operate in two modes, a low pressure, high volume mode and a high pressure, low volume mode.
Additionally, pumps have been developed that operate in two stages. In a first pump stare on a pump backstroke, air is pumped from a first chamber into a second pump chamber to prepressurize the air in the second pump chamber. Then, on a compression stroke, the prepressurized air in the second chamber is pumped into the tire. Such dual stage pumps therefore pump more air into a tire per stroke than a single stage pump. The present invention includes both types of pump features, and is thus a dual stage, dual mode pump.